Municipal solid waste is burned in waste-to-energy (WTE) plants, also known as trash-to-steam facilities, to produce usable energy in the form of either steam or electricity. Most modern WTE plants consist of six sections: the charging chute, the furnace, the boiler, the dry scrubber, the electrostatic precipitator and the ash extractor.
Municipal solid waste is delivered to the WTE plant by trash trucks where it is either placed directly into the charging chute or it is temporarily stored in a refuse pit for delivery to the charging chute at a later time.
The solid waste is burned at combustion temperatures in the range of 1,800.degree. F. to 2,000.degree. F. The residue remaining after the burning of the waste is referred to as ash. The ash is deposited in an ash extractor. The hot gases generated during combustion are directed to a boiler to create the steam used to drive the generators which produce electricity. However, before these hot combustion gases can be released into the atmosphere, they must be treated to remove small particulate and gaseous (SO.sub.2 etc.) combustion products. This is normally achieved by routing the gases through a dry scrubber and an electrostatic precipitator or bag house. The particulate matter which is removed from the gases at these processing units is referred to as fly ash. The fly ash is then conveyed to the ash extractor where it is mixed with the ash from the furnace.
The ash collected from the extractors can contain up to 40% moisture. Since the cost of a material deposited in a landfill is based upon its weight, the moisture content of the ash amounts to a substantial portion of disposal costs. It is therefore highly desirable to remove as much of this moisture as possible before the ash is shipped to the landfill.
An attempt is made to dewater the ash by mechanical means. A hydraulic ram pushes the moisture laden ash from the extractor up an inclined ramp. This procedure removes only a small portion of the moisture content of the ash. After this point, only oversized materials (e.g., mufflers, washing machines, propane cylinders, etc.) and magnetically separated ferrous metals are removed. The remaining ash is then eventually shipped to a landfill site for disposal.
It is highly desirable therefore to remove as much of the moisture as possible before the physical separation steps. An ideal location is at the place where all the ash is first gathered, the ash extractor. However, with its very high temperatures and high pH values, the ash extractor is a hostile environment for the use of conventional flocculant chemicals. It is thus an object of this invention to provide the art with a method for dewatering moisture laden ash within the ash extractor of a WTE plant.